While, in general, the present invention is specifically directed to electric vehicles of the sort that are, essentially, passenger vehicles or cargo vehicles such as vans and light trucks, it will be kept in mind that the present invention is equally adapted for use with such other electric vehicles as electric golf carts, fork lift trucks and other industrial trucks and pallet lifters, and the like. However, as discussed in greater detail hereafter, the present invention particularly lends itself to commercial applications wherein electric vehicles such as passenger vehicles and on-road cargo vehicles may recharge their batteries in much the same manner as present day vehicles having internal combustion engines re-fill their fuel tanks. Thus, a charging station for electric vehicles in keeping with the present invention may be found at street corners, along highways, and so on.
There are presently a number of experimental electric vehicles of the passenger type. Almost universally, however, those vehicles are extremely inefficient, carry very heavy batteries, and at best have very limited range of perhaps 100 or 200 km before the batteries need to be recharged. Significant research is being carried on throughout the world to develop new batteries which have much higher power per unit weight, and higher capacity, so as to allow faster and more long-ranging vehicles to be developed; and the present invention recognizes that as such vehicles reach the road either experimentally or particularly as commercial vehicles, there will be a much greater requirement for facilities to recharge them. Of course, such charging stations must be capable of delivering charging power to the batteries safely, quickly, and economically.
It follows that such charging stations must be capable of being controlled in such a manner that different batteries, having different capacities and even different terminal voltages--or, for that matter, being of different types--must be accommodated at the charging station for delivery of charging power. That means that there must be sufficient control either within the charging station or associated with the batteries to be charged, to permit such charging conditions; and as well, the charging station must be equipped in such a manner as to be compatible with the electric vehicles. Obviously, for commercial installations, means must also be provided to measure the amount of power being delivered and to arrive at a monetary charge to be paid by the consumer. The specifics of that issue are beyond the scope of the present invention.
Presently, electric vehicles are often equipped with an on-board charger associated with the battery, whereby slow charging--for example, overnight--of the battery may be accomplished from an ordinary electrical outlet. It may also be that the garage in which the vehicle is stored may be equipped with a stationary charger which may otherwise be the same as an on-board charger, but whereby more than one vehicle may be charged--however, usually only one at a time. These two methods are the ones which are most often found in electric over-the-road vehicles, while the second alternative noted above is most usually found in industrial charging installations for fork lift trucks and the like. Other electric vehicles such as golf carts may have removable battery trays which are taken from the vehicle and charged while a duplicate battery tray is placed in the vehicle to continue its useful working employment. Clearly, for electric passenger vehicles, and the like, the mass and weight of batteries required to power the vehicle--as well as the cost of the batteries--preclude any consideration of removable battery trays.
At present, most electric vehicles--particularly commercial and industrial vehicles such as fork lift trucks, golf carts, and the like--employ lead acid batteries. Other prospective and experimental vehicles, at least in the near future, may employ nickel cadmium, nickel iron, or nickel metal hydride batteries, with other batteries such as liquid sodium being further over the horizon.
The present invention, however, will accommodate all of those circumstances of battery charging for all kinds of electric vehicles, such as those discussed above.
Reference is made to co-pending U.S. patent applications Ser. No. 07/253,703 filed Oct. 6, 1988 and Ser. No. 07/676,523 filed May 2, 1991, for in depth discussions of fast battery charging and discussion of the battery chargers having advanced features whereby very rapid and safe battery charging is assured. Both of those co-pending applications are assigned to a common assignee herewith, with a common inventor as herein. The chargers of those inventions are capable of recharging quality traction or SLI batteries in 10 to 20 minutes. However, the energy requirement of an electrical automobile, in particular, may be in the range of from 20 to 50 kWh, and to deliver that energy in a short time requires that the charger have a high power rating, for example in the range of 100 to 300 kW. Obviously, chargers having power ratings of 300 kW have to be strategically located and properly connected into the electrical distribution grid. Such chargers may be found in charging stations in keeping with the present invention in typical locations such as ordinary service stations, fleet depots, and perhaps even in such locations as parking lots and the like.
However, as noted above, electric vehicles including electric automobiles and delivery vans and the like, are far from standardized as to the battery capacities and voltages that are built into them, and will probably continue in that same mode. For example, an experimental vehicle identified as IMPACT.TM. produced by General Motors has a 320 volt battery with a capacity of 45 Ah; whereas the PANDA ELETTRA.TM. produced by Flat carries a 72 volt battery, but has a capacity of 185 Ah.
What the present invention provides is a universal charging station at which a wide variety of electric vehicles may be charged, over a wide range of parameters. Of course, a number of preconditions apply, including the requirement that the vehicle to be charged must be equipped with a compatible power connector, and the obvious requirement that the charging station must be capable of providing a DC voltage at a sufficient level for any given vehicle, and at high current rates. Because of the nature of the charging station, signals will pass from the battery being charged to a power controller in the power section of the charging station, so at least a minimal accommodation for signals which are at least indicative of the voltage of the battery at any instant in time must be made. Of course, if the entire installation including the power delivery section of the charging station and the control means which controls the power section (and which may be specific as to the battery to be charged) are in keeping with the teachings of the co-pending applications noted above, then assured delivery of the maximum power in the shortest possible time to the battery will be achieved. Otherwise, the charging station of the present invention will still operate, but there will be no certainty as to optimum performance.
To that end, the present invention provides a charging station for electric vehicles that are equipped with a rechargeable battery, a traction motor and a traction controller for said traction motor, where the charging station comprises the following principle components:
A power section; a power controller section; a power connector for connecting the power section to an electric vehicle for recharging the battery thereof; an interface between said charging station and said electric vehicle; power cables capable of carrying high charging currents from the power section through the power connector to the electric vehicle; signal cable means capable of carrying control signals between the power controller section and the electric vehicle; and lockout means.
The power section is capable of delivering high charging currents at the requisite charging voltage for the battery being charged within predetermined limits of power to be delivered. The rate of delivery of the charging current is controllable.
The power section comprises a power source, a rectifier, and a switching inverter module; and each of the power controller section and the inverter module are fast acting so as to be able to turn delivery of the charging current on and off in less than a few milliseconds. More generally, the power section comprises a power source rectifying means, and means for controlling the flow of charging current to the rechargeable battery.
The signal cable carries signals from the battery to the power controller that are at least indicative of the voltage of the battery at any instant in time. At least the power cables and the signal cable means are associated with the interface.
Means are provided for measuring the resistance free voltage of the battery during intervals when delivery of said charging current to said battery has been turned off. Thus, operation of the power controller section may be affected by the resistance free voltage; and thereby operation of the switching inverter module or other means for controlling the flow of charging current to the battery, and of the charging station, may be controlled as a function of the resistance free voltage of said battery.
The lockout means of the charging station is adapted to preclude delivery of charging current to the battery except when the lockout means is locked closed. The lockout means is conveniently associated with said power connector.
Thus, operation of the charging station to recharge a battery in an electric vehicle is contingent upon the lockout means being locked closed so as to assure flow of charging current and control signals on their respective cables, and the charging operation is controlled so that the power being delivered is within the predetermined limits. Of further significance is the safety aspect of the lockout means, whereby the physical and electrical design of the power connector may be such as to assure that the operator will not be able to contact--or be exposed to--high voltage terminals connected to the battery or to the charging station.
In a particular type of charging station in keeping with the present invention, which may be such that the charging station will provide optimum performance, the charging station will be adapted to communicate with an on-board charge controller located within the vehicle, and which is adapted to control the rate of delivery of charging current to the battery. In that case, the charge controller is specific as to the battery to be charged so that its operating functions are contingent upon the type of battery to be charged, its nominal voltage and its nominal electrochemical energy capacity. The charge controller is adapted to pass signals via the signal cable means to the power controller section. Thus, operation of the power controller section is contingent upon the nature of signals received by it from the charge controller, and thereby operation of the charging station is controlled and is battery specific.
In the usual circumstances, the interface and the power connector are physically associated with each other. Indeed, the interface and the power connector may be one and the same thing. Moreover, in the most simple installations where operation of the battery charging station is not battery specific, the signals relating to the resistance free voltage of the battery may be passed over the charging current cables, thereby obviating the neccessity for separate signal cables in such circumstances.